The present invention relates to an exposure controlling apparatus, and more particularly to an exposure controlling apparatus for controlling the exposure amount of an image copying apparatus such as an automatic photographic printer for printing an image on a copying sensitive material from a color original picture, particularly on a color print paper from a color film. Description of the Related Art:
In general, when a color image is reproduced on a copying sensitive material from a color original picture, exposure amount is determined for the respective colors of red (R), green (G), and blue (B) by measuring the integral transmittance (or reflection) density of the R, G and B light by using a photometric device having color separation filters constituted by dyed filters and deposited filters. In order to determine exposure amount accurately, it is necessary to photometrically determine the exposure amount which actually contributes to the sensitization of the copying sensitive material. For this purpose, it is necessary to make the spectral sensitivity distribution of the photometric device coincide with the spectral sensitivity distribution of the copying sensitive material. The spectral sensitivity distribution of the copying sensitive material is asymmetrical about a wavelength at which sensitivity becomes maximum. With dyed filters and deposited filters, however, in order to fabricate them in such a manner that the transmittance distribution becomes asymmetrical, it is necessary to combine a multiplicity of filters, so that it is difficult to mass produce them and also difficult to fabricate them with a high degree of accuracy.
Accordingly, in photo-resist exposure apparatus, a technique is known in which the spectral sensitivity distribution of a photometric device is made to coincide with the spectral sensitivity distribution of a copying sensitive material by separating the light from an original picture into spectral components and effecting processing by adding weight to the separated components. Japanese Patent Laid-Open No. 88624/1983 discloses a photo resist exposure apparatus in which the aforementioned processing is effected by using a diffraction grating, a convergent optical system, and a photo-detector. However, a complicated mechanism is required so as to ensure that spectral sensitivity characteristics will not change due to the relative arrangement of these optical elements. Japanese Patent Laid-Open No. 95525/1986 discloses a photo resist exposure apparatus in which a multiplicity of interference filters are disposed instead of the aforementioned diffraction grating, the light transmitted through an original picture is separated into spectral components, and processing is effected by adding weight to the separated components. However, since the multiplicity of interference filters are required, a problem exists in that in cases where the number of photometric wavelengths is large, it is difficult to mass produce the interference filters by maintaining the spectral accuracy of the filters. Also, there is an additional problem in that since the separated components obtained from the interference filters exhibit a broad spectral distribution, even if a weighting addition is merely effected, the accuracy would be insufficient for the purpose of this application. In addition, with respect to color photographic printers, Japanese Patent Laid-Open No. 134353/1989 discloses a technique in which light from an original picture is subjected to spectral separation using a prism and a diffraction grating or a spectral filter, and an image of a part of a copy original is formed on a panel of a photoelectric sensor into the configuration of a slit. In this technique, different photometric positions are represented by rows of the panel, while spectral light corresponding to the photometric positions is converted to electric signals by columns of the panel. In this technique, the same problem as the one described above is encountered since the diffraction grating or the spectral filter is employed. Furthermore, since the light is separated into a multiplicity of spectral components of light, there is a problem in that the quantity of each spectral component of light is small, resulting in a shortage of the quantity of light. In addition, since the light is separated through diffraction by the use of the prism, there are drawbacks in that it is necessary to make the projected light into parallel light, that the apparatus becomes large in size, that the quantity of light decreases substantially since the light is separated into both rows and columns, and that a large difference in the quantity of light results for each spectrum, thereby making it impossible to effect photometry by using the same panel. Japanese Patent Laid-Open No. 142719/1989 also discloses the use of a prism or a diffraction grating, and a lens, and a two-dimensional array sensor. However, in this arrangement as well, the same drawbacks as those described above are encountered since the prism or the diffraction grating is used.
In order to overcome the conventional drawback of the quantity of light becoming short, it suffices to effect photometry by using spectral light having a wide half-width (e.g., 5-20 nm), or using light having greater diffusion than parallel light. Nevertheless, photometric values fail to express values measured by the spectral sensitivity distribution of the copying sensitive material owing to the broadening of the range of the photometric wavelengths.